The present invention relates to a procedure for the preparation of a new catalyst with application in hydrodenitrogenation and hydrodesulfurization of middle and heavy petroleum distillates. The catalyst object of the present invention is basically constituted by active metals and promoters, whose elements belong to groups VIII, VI, IVB of the periodic table, with specific properties for hydrodenitrogenation and hydrodesulfurization of middle and heavy petroleum oil fractions.
It is a fact that an urgent need exists to improve the surrounding ecology, which has been deteriorated by the past generations common practices. It is not until now, the second half of the second millennium, that people are aware of the damage caused to life and living species. Industries tend to be modernized and to establish cleaner production systems. In the same way, the refining industry is focused in producing cleaner fuels with higher quality and with minimum contents of contaminants such as sulfur, nitrogen and heavy metals. However, as the ecological regulations become more strict each day, it is urgent to have processes as well as catalysts performing more efficiently and at the same time able to comply with the new requirements.
Without any doubt, hydrotreating processes are industrially considered the most efficient in contaminants removal and are used for mostly all crude fractions such as gasolines, diesel, vacuum distillates and residues. In order to achieve maximum hydrodesulfurization, hydrodenitrogenation and hydrodemetallization at the given process conditions, it is necessary using catalysts with high activity and selectivity to these reactions. A given process operating with a particular catalyst having such characteristics, will not only remove nitrogen, sulfur and metals, but will improve other fuel properties such as color, stability to gum formation, etc.
The present invention relates to a procedure to prepare a new catalyst that is highly active and selective for hydrodenitrogenating middle and heavy oil fractions, and additionally provides a high hydrodesulfurization and hydrodemetallization capacity. This invention also relates with the process conditions for its industrial application.
Catalyst activity and selectivity is determined and affected by such factors as the nature and properties of the catalyst support, the catalytic agents, activity and selectivity promoters, as well as the preparation and activation method used.
Current catalysts in hydrotreating processes, namely, hydrodesulfurization, hydrodenitrogenation and hydrodemetallization of oil fractions incorporate metals from groups VIII and VIB of the periodic table, and are usually supported on metallic oxides such as alumina, silica or silica alumina. Occasionally, secondary promoters or additives are used such as halogens, phosphorous, borum, etc., enhancing the catalytic properties mainly for a dispersing effect on the active phase or the modifications resulting in the support""s physical and chemical properties.
Catalyst support properties play an important role in the catalytic activity. The first generation of catalyst supports had as their only function supporting or containing the active agents. During the 1970""s, studies developed on properties and effects of catalytic supports revealed that these could be designed for specific uses.
The support is generally a porous solid constituted by metallic oxides such as gamma alumina, delta alumina, etc.; silica, silica-alumina, titania, titania alumina; among others. A catalyst support used for hydrotreating catalysts can have different geometric forms, such as spheres, pellets, cylindrical extrudates, trilobular and tetralobular forms, etc., and also different sizes going from nominal sizes of {fraction (1/30)} to xe2x85x9 inch.
The method used to prepare catalysts also affects final catalyst activity and selectivity. Of the different methods used for preparing catalysts, (sol-gel, co-precipitation, etc.); the most efficient method known is support impregnation with a solution or solutions containing the active metals and/or promoters and/or additives. In this case, solutions must be very stable to prevent precipitation during impregnation stage and inside the matrix pores. It is necessary that the elements present in the solution be adsorbed and selectively distributed on both internal and external surface preventing its agglomeration.
U.S. patents relating to these procedures are the following:
U.S. Pat. No. 4,665,048 relates to a catalyst for hydrotreatment of oil and its fractions prepared by impregnation of ammonia solutions containing metals from groups VIII and VIB; and anions free derived from strong acids, followed by a drying and a calcination.
U.S. Pat. No. 4,769,129 relates to a method to hydrotreat hydrocarbon feeds using a catalyst containing vanadium sulfide prepared either in situ or outside the reaction zone. This method can be applied to gasolines, gas oils and residues for hydrotreatment, removing sulfur, nitrogen and metals.
U.S. Pat. No. 4,780,193 describes a process for hydrotreating catalytic cracking feeds at temperatures lower than 390xc2x0 C. and pressures higher than 12,000 KPa, which improves cracking of feeds to produce high octane gasolines. Desulfurization taking place with this process, reduces SOx emissions on the catalytic cracking system, and also hydrodenitrogenation takes place as result of the high pressures used.
U.S. Pat. No. 4,886,594 relates to a catalyst formulation consisting on a hydrogenating agent, being a metal from group VIB of the periodic table and phosphorous component, laid on the surface of the support which is a refractory inorganic oxide, free from any zeolitic components. This catalyst is specially used for hydrodenitrogenation and hydrodemetallization of high sulfur content feeds.
U.S. Pat. No. 5,009,768 describes an invention relating to a hydrocatalytic process for vacuum gas oil hydrotreatment, residual feed or a combination of these, in the presence of 100 ppm V and Ni, at moderate partial pressures. The process consists in two or more stages using feed demetallization at levels lower than 10 ppm vanadium and nickel, and hydrodenitrogenation and hydroconversion by means of a combined catalyst bed. The hydrotreated product is then submitted to a catalytic cracking to obtain gasolines.
U.S. Pat. No. 5,246,569 discloses a process and a catalyst for hydrocarbons hydrodesulfurization. The catalyst is prepared by impregnation to achieve 0.3 to 3 weight percent of P205; 4.5 to 6 weight percent of CoO and 19 to 23 weight percent of MoO5 and which is supported on alumina. Additionally, other organic or inorganic acids are incorporated to obtain more stable solutions.
The previous described technologies have been overwhelmed by the present invention; in catalyst properties, and its preparation procedure, as well as in catalyst performance, demonstrating a superior capacity for hydrotreating middle and heavy oil fractions.
The present invention is related to a catalyst with high catalytic activity and selectivity for hydrodenitrogenation, as well as a good hydrodesulfurization and hydrodemetallization activity on petroleum oil fractions, preferably middle and heavy fractions. This catalyst is obtained by impregnation of a solution containing metals from groups VIB and VIII of the periodic table. The support used is a porous refractory oxide whose metals belong to groups IIIA, IVA of the periodic table, or its combinations. Additionally, the support includes an additive in the form of an oxide whose metal belongs to group IVB of the periodic table. The impregnated material is thermally treated in an oxidizing atmosphere.
Once the catalyst is obtained, it is activated using presulfiding methods with sulfur compounds which easily decompose to generate the corresponding metallic sulfurs.
The catalyst described in the present invention is able to hydrotreat middle and heavy oil fractions, understanding that the term xe2x80x9chydrotreatmentxe2x80x9d includes hydrodenitrogenation, hydrodesulfurization and hydrodemetallization.
The catalyst comprises a support and metals which provide the physical and chemical properties to carry out such reactions at industrial hydrotreating conditions.
The support is formed of a refractory oxide, with alumina, silica, silica-alumina and their combinations. As the support base, it is preferably used gamma alumina, delta alumina, or a mixture of such alumina phases. The support preferably possesses specific properties of surface area, pore volume and pore volume distribution. Surface area properties range between about 180 m2/gram and about 350 m2/gram, preferably between about 200 m2/gram and about 300 m2/gram. The pore volume ranges from about 0.45 cm3/gram to about 1.0 cm3/gram, preferably between about 0.5 cm3/gram and about 0.7 cm3/gram. It is recommended to have pore volume distribution between 0% to 10% of the total pores of pores smaller than 50 xc3x85 size; 50% to 100% of the pores between 50 xc3x85 and 200 xc3x85, and 0% to 40% of the total pores of pores larger than 200 xc3x85, being the preferred distribution the following: pores smaller than 50 xc3x85 from 1% to 9%, 60% to 90% of pores between 50 xc3x85 and 200 xc3x85, and 3% to 30% of pores larger than 200 xc3x85. The average diameter resulting from this distribution is between 50 xc3x85 and 150 xc3x85, having preferred values between 60 xc3x85 and 100 xc3x85.
The support contains an additive to promote physical and chemical stability whose basic functions are dispersing and uniformly distributing the catalytic species with the function of promoting the hydrodenitrogenation, hydrodesulfurization and hydrodemetallization reactions of hydrocarbons constituting the middle and heavy oil fractions. This additive is formed by metals from group IVB of the periodic table such as titanium, zirconium; being preferred the use of titanium, which may be in its oxidized form as titania, in its rutile phase or anatase, or both. Titanium may be incorporated into the support by impregnation using an organic solution of a titanium compound, such as titanium butoxide in n-heptane, and under inert humidity-free conditions or by integration during support preparation either by integrating a titanium source such as titanium oxide into a bohemite binder or to pseudo bohemite or by coprecipitation.
The support may have different forms such as extrudates of various geometric forms, cylindrical or with two or more lobules; nominal sizes may range from {fraction (1/32)} inch to xc2xc inch, being preferred nominal sizes of {fraction (1/20)} to {fraction (1/10)} inch.
Integration of active metals is performed by impregnation of an aqueous solution. This solution is prepared in a basic or acid media.
The basic solution is prepared with a pH of 7.5 to 13, preferably of 9 to 12 based on the salts containing elements from group VIII, preferably Ni, as well as compounds containing elements from group VIB as Mo and W, preferably Mo. Metal salts from group VIII can be from nickel nitrates, nickel carbonate hydroxide tetrahydrate, nickel acetate, etc. It is recommended to use carbonate nickel hydroxide. The metal compounds used from group VIB are: ammonium molybdate, molybdic acid, molybdenum trioxide, etc.; while is better using molybdenum trioxide.
The solution is an acid media, and is prepared with pH of 1 to 6.5, preferably 1 to 5, from salts containing elements from group VIII, preferably Ni, as well as compounds containing elements from group VIB as Mo and W, preferably Mo. The metallic salts used from group VIII can be nickel nitrates, nickel acetates, etc., preferably nickel acetate. The metallic compounds used from group VIB are: ammonium molybdate, molybdic acid, molybdenum trioxide, etc., preferably to use molybdenum trioxide.
In both basic and acid solutions, an acid stabilizing agent can be introduced, preferably in acid solutions; which can be nitric acid, phosphoric acid, hydrogen peroxide, etc., preferably phosphoric acid, in the concentration necessary to keep pH in solution between 1 and 5.
Single solutions can be prepared from each of the nickel and molybdenum compounds and perform successive impregnations, each one followed by a thermal treatment involving drying at from about 100xc2x0 to 300xc2x0 C. and calcination at 350xc2x0 to 600xc2x0 C. Preferably, impregnation is performed with a solution containing all the desired elements, such as nickel and molybdenum. Impregnation can be performed by different methods such as immersing the support into the impregnating solution or by an incipient wetness with drops or spraying. Spraying is the preferred method.
Before proceeding with drying, the impregnated material must be aged for from about 1 to 24 hrs., preferably from about 3 to about 12 hrs, to assure a perfect distribution of the solution within the support porosity.
The impregnated material is then dried at temperatures of 100xc2x0 to 300xc2x0 C., preferably 110xc2x0 C. to 200xc2x0 C. for 1 to 24 hrs, preferably 3 to 12 hrs.
Once the impregnated material has been dried, calcination proceeds in oxidizing atmosphere, at temperatures between 350xc2x0 and 600xc2x0 C., preferably 400xc2x0 to 500xc2x0 C., for 1 to 12 hrs, preferably 3 to 6 hrs.
The resulting catalyst contains elements related in the following way: TiO2/(Mo+Ni), atomic ratio of 0.01 to 0.6, preferably 0.3 to 0.5, Mo concentrations from 5 to 30 wt %, preferably 8-15 wt % based on total catalyst weight, and Ni concentrations from 1 to 10 wt %, preferably 1.5 to 5 wt % based on total catalyst weight. The catalyst of the present invention has a surface area of 150 to 400 m2/g, preferably 170 to 300 m2/g; pore volume between 0.3 to 0.9 cm3/g; preferably 0.4 to 0.6 cm3/g, and pore diameters go from 40 to 100 Angstroms, preferably 55 to 80 Angstroms.
Before using the resulting catalyst, prepared as indicated before, it must be activated converting the metallic oxides to sulfides by presulfiding with well known feeds and industrial conditions.
The catalyst can be used in conventional fixed bed reactors, for hydrotreating feedstocks at 40 to 15 xc3x85PI gravity containing total nitrogen of 50 to 3500 ppm, basic nitrogen of 10 to 1000 ppm, sulfur of 500 to 35,000 ppm and metal contents (Ni+V) of 0 to 10 ppm.
Process conditions at which feeds are hydrotreated with the present developed catalyst range from 300xc2x0 to 400xc2x0 C. temperature, space velocity of 0.5 to 3.0 hrxe2x88x921, pressures of 40 to 100 Kg/cm2 and hydrogen/hydrocarbon ratio of 1000 to 3500 (scf/bbl).
In order to compare the catalytic activity of the catalyst of the present invention, a relative activity for each given reaction is used, and this is defined as the relation between the activity of the given catalyst and the reference catalyst. This ratio equals the corresponding of the reaction velocity constant in relation to the reaction velocity of a reference catalyst. In this way, reference activities for the total hydrodesulfurization reactions, the total hydrodenitrogenation reactions, the basic hydrodenitrogenation reactions and the hydrodemetallization, are calculated.